Fix narrow PWA layout on tablet with standalone width rules.

Allow any orientation in manifest, widen content and enable dual-column mode in installed apps on tablet viewports, with iOS display-mode fallback.

Co-authored-by: Cursor <cursoragent@cursor.com>

components/footer.tsx

@@ -6,7 +6,7 @@ function Footer() {
   return (
     <footer className="relative z-10 flex items-center justify-center gap-1 border-t border-border/40 bg-card/70 py-4 text-xs text-muted-foreground/80">
       <div
-        className={`${SITE_WIDTH_INNER} flex items-center justify-center gap-1`}
+        className={`site-content-shell ${SITE_WIDTH_INNER} flex items-center justify-center gap-1`}
       >
         <span className="italic">心诚则灵</span>
         <span className="text-muted-foreground/60">·</span>